1. Field of the Invention
The present invention relates to a system and method to control a powertrain of a vehicle, and in particular powertrain control during vehicle deceleration.
2. Background of the Invention
Transmissions are known that have over-running, or oneway clutches. In some applications, these clutches are used to enable certain types of vehicle shifts such as so-called non-synchronous gear changes. In some cases, the transmission input speed is less than the synchronous speed of the selected gear during situations in which the clutch is overrunning. To prevent such situations, an electric motor, coupled to the transmission through a torque synthesizing/distributing unit, is used to maintain the gear input speed at or near the synchronous speed. The torque synthesizing/distributing unit is an additional unit that has planetary gear sets and several clutches. Such a system is described in U.S. Pat. No. 6,019,699.
The inventors herein have recognized a disadvantage with the above approach. In particular, such a method uses an electric motor, which is not available on the majority of mass production vehicles. Adding such a motor can be a significant additional cost to the customer. Further, the above method also uses an additional torque synthesizing/distributing unit. This additional device adds further to the cost of the vehicle.